1. Field of the Invention
The invention involves the cleaning of a polycrystalline silicon body after it has been doped by a phosphorous diffusion process.
2. Description of the Prior Art
Polycrystalline silicon is widely used in the manufacture of integrated circuits and similar solid state devices. This material can be formed in various ways. One useful way is to deposit polycrystalline silicon as a layer onto an integrated circuit during its manufacture and to the dope, pattern or otherwise work this layer to form a part of the final integrated circuit structure.
Polycrystalline silicon layers are often formed undoped and then doped with a conductivity imparting material which as is known by those in the art as N or P type. Alternately, the layers of polycrystalline silicon are often formed doped with such N or P type material as it is deposited.
Phosphorous, which is an N type impurity is often the conductivity imparting material used in the manufacture of integrated circuits. This material can be included as the polycrystalline silicon is deposited. It can also be imparted to the polycrystalline silicon after it has been formed by either a thermal diffusion or ion implantation process.
Where a thermal diffusion process is used, all such gaseous phosphorus doping processed in silicon semiconductor fabrication technology require the introduction of phosphorus into the silicon by the following reaction: EQU 2P.sub.2 O.sub.5 +5Si=4P+5SiO.sub.2
The resulting elemental phosphorous is in solid solution in the silicon surface layer. The preferred chemical process for forming phosphorous pentoxide in the equation in the vapor phase is by reacting phosphorous oxychloride with oxygen by the following reaction: EQU 2POCl.sub.3 +1.5O.sub.2 =P.sub.2 O.sub.5 +3Cl.sub.2
The phosphorous halide is available as 99.9999% pure with respect to transition and alkali metals. Phosphine is also a source for forming phosphorous pentoxide by the following reaction: EQU 2PH.sub.3 +4O.sub.2 =P.sub.2 O.sub.5 +3H.sub.2 O
There are other less popular reactions for forming the phosphorous pentoxide that will not herein be discussed, but are known to those skilled in the art.
After the thermal doping process, the remaining silicon dioxide on the silicon surface is removed by conventional hydrofluoric acid etching. The next integrated circuit or the like processing will then continue as is appropriate. Up until recently this procedure caused no problem. However, with the movement into the highly dense integrated circuit submicron technology there has been encountered severe yield problems. We have found that the problems stem from an apparent residue that remains after the normal hydrofluoric acid etching.
It is therefore a primary object of this invention to overcome the yield problems in processing polycrystalline silicon bodies that are doped with phosphorous after deposition.
It is a further object of this invention to provide a cleaning process after the hydrofluoric acid etching that follows the phosphorous thermal diffusion process for solving the yield problems in the high density integrated circuit processing.